An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 13116 Search : far
Foucault pendulum
  آونگ ِ فوکو   
âvang-e Foucault (#)

Fr.: pendule de Foucault   

A → pendulum consisting of a heavy weight on a very long wire attached to a support, that shows the rotation of Earth. The support must be nearly frictionless in order that the pendulum can continue to swing freely for long periods of time. The pendulum will swing in the same plane as it started. The → Earth's rotation is reflected in the slow turning of the plane of the pendulum's motion, which appears to rotate through 360° in T hours. The rotation time is given by the expression: T = T0/sin φ, where T0 = 23.9344 hours is the → sidereal day and φ the → latitude of the place. At the poles the rotation period is 23h 56m 04s, and at the equator is ∞, i.e. the swing plane does not move. For regions near the equator it is very long; for example at Quito, the capital city of Ecuador, with φ = 00°15'S, it is 5485 days or more than 15 years! This phenomenon shows that the Earth is a → non-inertial frame.

The experiment was performed for the first time by the French physicist Léon Foucault (1819-1868) in 1851, who set up, in the Pantheon in Paris, a simple pendulum consisting of a lead ball weighing 28 kg, suspended by a fine steel wire 67m long. At the latitude of Paris, the pendulum takes 31h 47m 38s to complete a precession cycle; → pendulum.

Foucault's Marseille reflector
  بازتابگر ِ فوکو‌ی ِ مارسی   
bâztâbgar-e Foucault-ye Marseille

Fr.: réflecteur marseillais de Foucault   

The first functioning → reflecting telescope with a silvered glass mirror. It was built by Léon Foucault in 1826 for the Marseille Observatory. The mirror of 80-cm in diameter (f/d = 5) had an excellent quality. The telescope was used for a century as a visual instrument. Edouard Stéphan (1837-1923) used it from 1871 to 1884 to find 800 high-brightness galaxies, among which the → Stephan's Quintet. From 1906 to 1962 the telescope was used by Robert Jonckheere (1888-1927) to discover 3,350 new binary stars. In 1873, following an idea of Hippolyte Fizeau (1819-1896), Stéphan attempted to use it as an → interferometer to measure the diameter of a number of stars. In 1914 Charles Fabry (1867-1945) and Henri Buisson (1873-1944) used the telescope to obtain the first astronomical Fabry-Pérot interferogram, on the → Orion Nebula.

After the French physicist and optician Léon Foucault (1819-1868); Marseille (Observatory), the second largest city of France, located on the south east coast of the Mediterranean Sea, from L. Massalia, from Gk. Massalia; → reflector.

four
  چهار   
cahâr (#)

Fr.: quatre   

O.E. feower, from P.Gmc. *petwor- (cf. O.S. fiwar, Du. and Ger. vier, O.N. fjorir, Dan. fire, Sw. fyra), cognate with Pers. cahâr, as below, from PIE *qwetwor.

Cahâr, variant câr, from Mid.Pers. cahâr; Av. caθwarô, catur-; cf. Skt. catvārah; Gk. tessares; cognate with L. quattuor; E. four, as above.

four-dimensional operator
  آپارگر ِ چهار-وامونی   
âpârgar-e cahâr-vâmuni

Fr.: opérateur à quatre dimensions   

An operator defined as: ▫ = (∂/∂x, ∂/∂y, ∂/∂z, 1/(jc∂/∂t).

four; → dimensional; → operator.

Fourier analysis
  آنالس ِ فوریه   
ânâlas-e Fourier

Fr.: analyse de Fourier   

The process of decomposing any function of time or space into a sum of sinusoidal functions using the → Fourier series and → Fourier transforms. In other words, any data analysis procedure that describes or measures the fluctuations in a time series by comparing them with sinusoids. Fourier analysis is an essential component of much of modern applied and pure mathematics. It forms an exceptionally powerful analytical tool for solving various problems in many areas of mathematics, physics, engineering, biology, finance, etc. and has opened up new realms of knowledge.

After the French mathematician Baron Jean Baptiste Joseph Fourier (1768-1830), whose work had a tremendous impact on the physical applications of mathematics; → analysis.

Fourier coefficient
  همگر ِ فوریه   
hamgar-e Fourier

Fr.: coefficient de Fourier   

One of the coefficients an or bn of cos (nx) and sin (nx) respectively in the → Fourier series representation of a function. They are expressed by:
an = (1/π) ∫f(x) cos nx dx, for n≥ 0, summed over 0 to 2π
bn = (1/π) ∫f(x) sin nx dx, for n≥ 1, summed over 0 to 2π.

Fourier analysis; → series.

Fourier integral
  درستال ِ فوریه   
dorostâl-e Fourier

Fr.: intégrale de Fourier   

An integral used in the → Fourier transform.

Fourier analysis; → integral.

Fourier series
  سری ِ فوریه   
seri-ye Fourier

Fr.: séries Fourier   

A mathematical tool used for decomposing a → periodic function into an infinite sum of sine and cosine functions. The general form of the Fourier series for a function f(x) with period 2π is:
(1/2) a0 + Σ (an cos (nx) + bn sin (nx), summed from n = 1 to ∞,
where an and bn are the → Fourier coefficients, measuring the strength of contribution from each harmonic. The functions cos (nx) and sin (nx) can be used in this way because they satisfy the → orthogonality conditions. For the problem of convergence of the Fourier series see → Dirichlet conditions. The Fourier series play a very important role in the study of periodic phenomena, because they allow one to decompose a large number of complex problems into simpler ones. The generalization of this method, called the → Fourier transform, makes it possible to also decompose non-periodic functions into harmonic components. See also → complex Fourier series, → Parseval's theorem.

Fourier analysis; → series.

Fourier theorem
  فربین ِ فوریه   
farbin-e Fourier

Fr.: théorème de Fourier   

Any finite periodic motion may be analyzed into components, each of which is a simple harmonic motion of definite and determinable amplitudes and phase.

Fourier analysis; → theorem.

Fourier transform
  ترادیس ِ فوریه   
tarâdis-e Fourier

Fr.: transformée de Fourier   

A powerful mathematical tool which is the generalization of the → Fourier series for the analysis of non-periodic functions. The Fourier transform transforms a function defined on physical space into a function defined on the space of frequencies, whose values quantify the "amount" of each periodic frequency contained in the original function. The inverse Fourier transform then reconstructs the original function from its transformed frequency components. The integral F(α) = ∫ f(u)e-iαudu is called the Fourier transform of F(x) = (1/2π)∫ f(α)eiαxdx, both integrals from -∞ to + ∞.

Fourier analysis; → transform.

fourth contact
  پرماس ِ چهارم   
parmâs-e cahârom

Fr.: quatrième contact   

The end of a solar eclipse marked by the disk of the Moon completely passing away from the disk of the Sun.

From M.E. fourthe, O.E. féowertha, from four, from O.E. feower, from P.Gmc. *petwor- (cf. Du. and Ger. vier, O.N. fjorir, Dan. fire, Sw. fyra), from PIE *qwetwor (cf. Mod.Pers. cahâr, Av. caθwar-, catur-, Skt. catvarah, Gk. tessares, L. quattuor) + -th a suffix used in the formation of ordinal numbers, from M.E. -the, -te, O.E. -tha, -the; cf. O.N. -thi, -di; L. -tus; Gk -tos; → contact.

Parmâs, → contact; cahârom cardinal form from cahâr "four," cognate with E. four, as above.

fovea
  لکه‌ی ِ زرد   
lake-ye zard (#)

Fr.: fovéa   

A small depression, approximately 1.5 millimeters in diameter, at the back of the → retina. It forms the area of the most acute vision.

Contraction of fovea centralis, from L. fovea "small pit," of unknown origin.

Lake-ye zard, literally "yellow spot," from laké, → spot, zard, → yellow.

fox
  روباه   
rubâh (#)

Fr.: renard   

Any of several carnivores of the dog family, especially those of the genus Vulpes, smaller than wolves, having a pointed, slightly upturned muzzle, erect ears, and a long, bushy tail (Dictionary.com).

M.E., from O.E. fox "a fox;" cognate with O.Saxon vohs, M.Du. vos, O.H.G. fuhs, Ger. Fuchs, from Proto-Germanic *fuh-, from PIE *puk- "tail;" cf. Skt. puccha- "tail," Toch. B päkā- "tail."

Rubâh, from Mid.Pers. rôbâh (Sogd. ropas), Av. raopi- "fox." This Iranian word was borrowed into Nordic languages as Old Norse rew, Icelandic refur, Faroese revur, Swedish räv, Danish ræv, Finnish repo. The transmission would have taken place through Sarmatian or Alanic intermediaries (cf. Ossetic ruvas / robas "fox").

fractal
  برخال   
barxâl (#)

Fr.: fractal   

A geometrical or physical structure that repeats itself or nearly repeats itself on many different scales of magnification.

From Fr. fractale, term coined by Benoit Mandelbrot (1975), from frac(tus) "broken, uneven", → fraction, + -ale-al.

Barxâl, from barx, → fraction, + -âl-al.

fractal cosmology
  کیهانشناخت ِ برخالی   
keyhânšenâxt-e barxâli

Fr.: cosmologie fractale   

The postulate that the concentrations of matter in the Universe follow a → fractal structure over a wide range of scales.

fractal; → cosmology.

fractal structure
  ساختار ِ برخالی   
sâxtâr-e barxâli

Fr.: structure fractale   

A → hierarchial structure that can be likened to fractals.

fractal; → structure

fraction
  برخه   
barxé (#)

Fr.: fraction   

A rational number of the form a/b where a is called the numerator and b is called the denominator.

From L.L. fractionem (nom. fractio) "a breaking in pieces," from frangere "to break," from PIE base *bhreg- "to break" (cf. Goth. brikan, O.E. brecan "to break;" Lith. brasketi "crash, crack").

Barxé, from barx "lot, portion," variant bahr, from Mid.Pers. bahr "lot, share, portion," Av. baxəδra- "portion."

fractional
  برخه‌ای   
barxe-yi

Fr.: fractionnaire, fractionné, partiel   

1) Math.: Pertaining to fractions; constituting a fraction.
2) Chemistry: Of or relating to any process by which parts of a mixture are separated by exploiting differences in their physical properties, such as their boiling points, solubility, or other characteristics.

fraction; → -al.

fractional sky coverage
  پوشش ِ برخه‌ای ِ آسمان   
pušeš-e barxe-yi-ye âsmân

Fr.: couverture partielle du ciel   

The portion of the 4π → steradians of the sky that a radiotelescope can observe from a given location on Earth over a 24-hour time interval.

fractional; → sky; → coverage.

fractionate
  برخاندن   
barxândan

Fr.: fractionner   

1) To break something up into smaller parts.
2) To separate a mixture into ingredients or portions having different properties, as by distillation or otherwise.

From → fraction + -ate a suffix forming verbs or nouns, from L. -atus, -ata, -atum.

Barxândan, from barx, barxé, → fraction, + -ândan suffix of transitive verbs.

<< < -es -iv -ti 21 a p abe abs abs aca acc acc acr act ada adh Adr aer aga air Alf Alg alk Alp alt alu amm ana And ang ani ano ant ant Ap apo app app Aqu Arc arg arr asc ass ast ast asy atm ato att aur aut axi B-m bad Bal bar bar Bay Bed ber Bet bif bim bin bio bis bla ble blu Bod Bol bor bou Bra Bre bro bul C-t Cal Cam can car Car Cas cat cav cel cen cer Cha cha Cha che chl Cir cir cir Cla cli clo clu co- coc coh col col col Com com com com com com com com Com con con con con con con con con con con con con coo Cor Cor cor cos cos cos Cou cou Cra Cre cri cro cub cur cyc cyl Dan dat Dav de- Deb dec dec dee def deg del Den den der det deu dew dic dif dif dil Dip dir dis dis dis dis dis diu dod Dop dou Dra dua dus dwa dyn DZ Ear ecc eco edi EHB Ein ela ele ele ele ele ell eme emp end Eng ent epi equ equ era ESP eth Eur evi exa exc exe exi exp exp ext ext ext fac fal far fec Fer fer fie fin fir fis fla Flo flu fog for for Fou fra fre fre Fro fun G s Gal gal gal Gar gau geg gen geo geo geo ger gla gly gra gra gra gra gra Gre gro GYR Had Hal hap Har HD hea hel hel Hen Her hex hig Hil hol Hoo hor hou Hub hum hyb hyd hyd hyp hys ide ign ima imp imp in- inc Ind ind ine inf inf inf ini ins ins ins int int int int Int int int int inv ion iri irr iso iso iso Jea Jor jum K c Kep Ker kin kno lab Lam Lan Lap las lat Le lef len lev lig lig lin lin lin liq Lit loc log lon lou LS lun lun Lym M s Mag mag mag mag mag mag maj man Mar mas mas mat May mea mec mel mer mes met met met mic mid mil Min Mir mix mod mod mol mon mor mov mul mur mys nan nat nav nec Nep neu New New NGC nob nom non non nor nos nuc nuc num nut obj obl obs occ oct off oli oni ope opp opt opt orb ord org orp osc out ove oxi P-w pal par par par par Pas pat pej per per per per per per pha Phe pho pho pho phy pin pla Pla pla pla pla plu poi pol pol Pol pol por pos pot Poy pre pre pre pre pri pri pri pro pro pro pro pro pro Psa pul pum Q i qua qua qua qua R A rad rad rad rad rad rad Ram Ran rat rea rea rec rec red red ref ref reg rei rel rel rem rep res res res ret rev Rho Rie ril riv rog Ros rot rul S A Sag sam sat sca sca Sch Sco Sec sec sec seg sel sem sen set Sha sha shi sho sid sig sim sin Sir ske sli Smo soc sof sol sol sol sol sou sou spa spe spe Spe spe sph spi Spi spr sta sta sta sta sta ste ste ste Sto str str sub sub sub suc sun sup sup sup sup sur swa syn syn tac tas tel tem ter tes the the the the thi thr tid til tip ton tor tou tra tra tra tra Tri tri tru tsu tur two Typ UHE ult unc uni uni uni upg ura uti val var vec Vel ver Ver vie Vir vis vis vol W-R war wav wav wea Wei wha wid win WN3 Wol wri xen yok zen zij > >>